Parallel Processing of Stimulus Features during RSVP: Evidence from the Second Response

Article excerpt

When observers are asked to report a feature of a single target displayed in rapid serial visual presentation, they frequently make errors. Most frequently, a feature from the to-be-reported dimension pertaining to a stimulus presented near the target is reported. These migrations are so-called illusory conjunctions in the time domain. From parallel models, it is proposed that during the presentation of the series, the response features of the stimuli are extracted. If a high rate of presentation does not enable proper binding processes, the system could base its response on sophisticated guessing on the basis of the relative levels of activation of the available response features. However, the multiple extractions assumption has not received direct empirical support. We report two experiments in which the observers had to report their first and second response candidates. This double response paradigm makes it possible to test the assumption that more than one response feature is available for making a response. Furthermore, the application of the constant ratio rule (following Botella, Barriopedro, & Suero's, 2001, model) to the first responses allows predictions for the ratios between choices of the items for the second responses. The correlations between the observed and the predicted response proportions were .887 and .956 in the two experiments. This high predictive capacity indicates, first, that the observers have more than one response available, among which to choose, and second, that the choice among responses is determined largely in the same way for both first and second responses. Nevertheless, the small errors in prediction are further reduced if a proportion of pure guesses is assumed in the second responses. These are probably due to memory losses, misidentifications of the features, and other factors impairing performance in second responses in comparison with first responses.

The last two decades have witnessed a remarkable increase in interest in human temporal capacity limitations in processing environmental stimuli, and effects on performance when these limits are exceeded (Shapiro, 2001). One manifestation of such limits, as viewed from the conceptual framework of attention, has been the difficulty in noticing stimulus repetitions if the two occurrences are close in time (repetition blindness or RB; Kanwisher, 1991). Another manifestation is the difficulty in identifying the second of two targets when the second is presented temporally close to the first (attentional blink or AB; Raymond, Shapiro, & Arnell, 1992). A similar phenomenon is the slowing of responses to me second of two targets if tiiey are close in time (psychological refractory period or PRP; Pashler & Johnston, 1998). All of these phenomena indicate tiiat during episodes in which cognitive processes are engaged in certain activities, capacity limits create difficulties in performing other activities or the same activity with other stimuli. When these capacity limits are exceeded by a high rate of information presentation (as in conventional tasks that use rapid serial visual presentation, or RSVP) the above mentioned phenomena (i.e., RB, AB, and PRP) show up, all of which reveal different types of performance decrements.

A similar phenomenon, although much less studied, is the report of a mixture of features between stimuli presented in close temporal succession, sometimes called intrusions or illusory conjunctions in the time domain (Botella, Barriopedro, & Suero, 2001; Botella & Eriksen, 1992; Cohen & Wry, 1989; Gathercole & Broadbent, 1984; Keele, Cohen, Ivry, Liotti, & Yee, 1988; Kikuchi, 1996; Lawrence, 1971; McLean, Broadbent, & Broadbent, 1983). We identify stimuli by building integrated percepts or bound representations of significant units that give sense to the world around us. When presentation rates are within some "natural" range, me extracted features can be properly bound into representations of the presented objects. …